Re: [PATCH v4] ARM: boot: Obtain start of physical memory from DTB

From: Ard Biesheuvel <ardb@kernel.org>
To: Geert Uytterhoeven <geert+renesas@glider.be>,
	Nicolas Pitre <nico@fluxnic.net>
Cc: "Arnd Bergmann" <arnd@arndb.de>,
	"Russell King" <linux@armlinux.org.uk>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	"Chris Brandt" <chris.brandt@renesas.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Eric Miao" <eric.miao@nvidia.com>,
	"Dmitry Osipenko" <digetx@gmail.com>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	"Marek Szyprowski" <m.szyprowski@samsung.com>
Subject: Re: [PATCH v4] ARM: boot: Obtain start of physical memory from DTB
Date: Tue, 14 Apr 2020 10:06:56 +0200	[thread overview]
Message-ID: <CAMj1kXFAEOWGgmMT4SMP=QafcT54mzMekLjm3wMTN8M4psNSKw@mail.gmail.com> (raw)
In-Reply-To: <CAKv+Gu8q2bAVMRLSc-Ae=hxhg3sbvpfuaMJ_nx4FZFvegNZ+9w@mail.gmail.com>

On Wed, 25 Mar 2020 at 17:40, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Fri, 20 Mar 2020 at 15:43, Geert Uytterhoeven
> <geert+renesas@glider.be> wrote:
> >
> > Currently, the start address of physical memory is obtained by masking
> > the program counter with a fixed mask of 0xf8000000.  This mask value
> > was chosen as a balance between the requirements of different platforms.
> > However, this does require that the start address of physical memory is
> > a multiple of 128 MiB, precluding booting Linux on platforms where this
> > requirement is not fulfilled.
> >
> > Fix this limitation by obtaining the start address from the DTB instead,
> > if available (either explicitly passed, or appended to the kernel).
> > Fall back to the traditional method when needed.
> >
> > This allows to boot Linux on r7s9210/rza2mevb using the 64 MiB of SDRAM
> > on the RZA2MEVB sub board, which is located at 0x0C000000 (CS3 space),
> > i.e. not at a multiple of 128 MiB.
> >
> > Suggested-by: Nicolas Pitre <nico@fluxnic.net>
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> > Reviewed-by: Nicolas Pitre <nico@fluxnic.net>
> > Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> > ---
> > v4:
> >   - Fix stack location after commit 184bf653a7a452c1 ("ARM:
> >     decompressor: factor out routine to obtain the inflated image
> >     size"),
> >
>
> Apologies for the breakage. I was aware of the existence of this
> patch, but I didn't realize it was accessing LC0 early on to find the
> stack pointer value.
>
> Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
>

OK, so one thing I did notice when playing with this code is that the
phys/virt patching code requires that 'PHYS_OFFSET - PAGE_OFFSET' is a
multiple of 16 MB, and so this needs to be taken into account by this
change as well, given that PHYS_OFFSET is based on the placement of
the uncompressed kernel in the physical address space.

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